The present invention relates generally to a process for the production of sulfur containing organosilane compounds. The present invention further relates to a method of using sulfur containing organosilane compounds in bituminous compositions.
The composition of the invention can be broadly assigned to organic silicon containing compounds. More specifically, these reaction products are comprised of linear silicon-sulfur containing compounds, cyclic-organosilanes, silmethylenes, polycyclic silthaines, polysilthianes, cyclic and cluster silicon-sulfur compounds, and their mixtures.
Numerous methods have been disclosed in the art for the preparation of sulfur containing organosilicon compounds. U.S. Pat. No. 2,567,724 to Moody discloses a process for making polysilthianes consisting of hexamethyl cyclotrisilthiane and tetraphenyl cyclotristhiane. U.S Patent No. 2,590,039 to Richter et al. discloses the reaction of organosilicon halides with organo-dithiols. U.S. Pat. No. 6,472,481 to Luginsland et al. discloses a process for making linear polyorganosiloxanes. U.S. Pat. No. 6,211,345 to Weller et al. discloses a process for synthesizing sulfur-containing norborane silanes specifically. U.S. Pat. No. 6,384,256 to Backer discloses a process in which an alkali metal hydroxide compound reacts with a sulfide compound to form a polysulfide mixture and the subsequent reaction of polysulfides with a silane compound produces sulfur containing organosilicon compounds.
All the above patents involve the use of monosilanes or a single type of silane—or more specifically siloxanes.
Herzog et al. (2000, J. Organomet. Chem. V602, pg. 193-207) discusses the synthesis of cyclic silthianes using disilanes and two different types of silanes.
The “Direct Process” or “Rochow Process” refers to an indirect way of making the chlorosilanes from Me—Cl via the Grignard reagent RMgCl. This process is described by Rochow in U.S. Pat. No. 2,380,995 and in U.S. Pat. No. 2,488,487 by Barry et al. As a result of Direct Process several chlorosilane monomers and oligomers are produced in side reactions. The byproduct monomers typically consist of a mixture of methyltrichlorosilanes, trimethylcholorosilanes, and methydichlorosilanes. The oligomers include a high boiling blend of disilanes, silmethylenes and polysilalkylenes also known as “Direct Process Residue (DPR).” The high boiling fraction may also contain particulate silicon and metals or compounds thereof. The Direct Process generates one of the largest organosilane by-products streams.
Examples of sulfur containing organosilanes are found in U.S. Pat. No. 6,350,797 to Weller, U.S. Pat. No. 5,580,919 to Agostini et al. and U.S. Pat. No. 5,674,932 to Agostini et al. These compounds are utilized as additives and coupling agents, in rubber mixtures and tires to improve tread wear and better wet skid resistance on asphalt pavement surfaces.
Bituminous materials, sometimes referred as bitumen and also known as asphalt binder, is used as a binder in asphalts to pave roads and other surfaces and is used in other construction materials such as roofing materials, coatings, waterproofing applications, sealants, etc. Examples of bitumen that may be used in compositions and methods of present invention include natural bitumens, pyrobitumens, and artificial bitumens. Bitumens that are particularly preferred are those used for roadways, such as asphalt or malta.
Asphalt binders are frequently used in applications where there can be a wide variation in environmental conditions, particularly in temperature when used in pavement applications. Consequently the properties of asphalt binder in high and low temperature conditions are a concern. Asphalt gets hard and brittle at low temperatures, and becomes soft at higher temperatures. More specifically, in hot conditions/climates or under sustained loads, such as slow traffic or parked heavy loads, asphalt binders behave like a viscous liquid. In cold conditions/climates or under rapidly-applied loads such as fast moving heavy loads, asphalt binders behave like an elastic solid. Under either condition, when subjected to excessively heavy loads such as heavy truck traffic, asphalt can become brittle and crack and rutted.
Resistance to fatigue and impact and the adherence of the asphalt binder to the aggregate are crucial in paving applications. Some asphalt binders may require a relatively elastic behavior, such as high traffic areas and high loads. Typically in order to improve their elastic properties polymer modifiers, sulfur crosslinkers, and other additives are used with asphalt binders.
The present invention provides a process for the production of sulfur containing organosilane compounds from disilanes, monosilanes, and mixtures thereof including by-products and waste streams.
Further the present invention provides for the use of sulfur containing organosilane compounds in asphalt compositions as additives and/or crosslinking agents.